Association between respiratory sinus arrhythmia and reductions in startle responding in three independent samples.

Evidence suggests that respiratory sinus arrhythmia (RSA) may be an important indicator of physiological flexibility. However, few studies have examined the relation between RSA and defensive habituation, a process contingent on physiological flexibility. In three independent samples, habituation was defined as the time course of 9 startle responses. In Sample one and two, startle was recorded (1) while shock electrodes were attached to participants' and (2) before a threat-of-shock task. In Sample three, startle was recorded without these two components. In the first two samples, startle magnitude significantly decreased over time but in Sample three, startle only decreased at a trend level. Further, low RSA was associated with less of a reduction in startle magnitude over time within the first two samples, but was unrelated to startle reduction in the third. This suggests that low RSA is associated with less habituation to contextual anxiety, which may reflect difficulties regulating anxiety.